The More Exposure to Diesel Exhaust, the Greater the Risk of ALS, Harvard Study Suggests

The more a person is exposed to diesel exhaust, the greater the chance they will develop ALS, a Harvard University study on Denmark reports.

The team will present the findings at the American Academy of Neurology‘s 70th Annual Meeting in Los Angeles, April 21 to 27. The presentation is titled “Amyotrophic Lateral Sclerosis and Exposure to Diesel Exhaust in Denmark.”

Scientists believe both genetic and environmental factors play a role in the development of ALS. Until the Harvard study, the only specific environmental factor that researchers had linked to the disease was smoking.

“There is some suggestion from previous studies of occupation that workers in jobs with higher exposure to diesel exhaust may have a higher risk of ALS,” Dr. Aisha Dickerson of the Harvard T.H. Chan School of Public Health in Boston said in a press release. “However, no studies have directly looked at the relation between diesel exhaust exposure during different time points in life and ALS,” said Dickerson, the author of the study.

The team decided to see if exposure to the exhaust would increase a person’s risk of developing ALS over time.

The study covered 1,639 ALS patients in the Danish National Patient Registry. The patients, whose average was 56, were added to the registry between 1982 and 2013.

For each ALS patient, researchers rounded up 100 age- and sex-matched controls.

The team used patients’ employment history to estimate their diesel exhaust exposure five and 10 years before their ALS diagnosis. They did the same with the controls.

They divided the participants into four groups, depending on what they estimated was their diesel exposure rate.

Jobs that they figured would have high diesel exposure included service station attendant, bus driver and construction worker.

A key finding was that men exposed to a lot of diesel exhaust 10 years before their ALS diagnosis were 20 percent more likely to develop the disease than men who weren’t.

Researchers calculated that one group of men had a more than 50 percent chance of being exposed to a lot of diesel exhaust. Those in it were 45 percent more likely to develop ALS at both five and 10 years than participants who were not exposed to a lot of exhaust.

The findings were similar to those of a Dutch group’s study, which reported that long-term exposure to traffic-related air pollution increased people’s susceptibility to ALS.

Interestingly, the association that the Harvard team found between long-term diesel exposure and ALS did not apply to women. This might be because job tasks in certain fields differ substantially between sexes, the team said.

“The overall risk of developing ALS is low, but our findings suggest that the greater the exposure to diesel exhaust, the greater the risk of developing ALS,” Dickerson said. “This type of exposure deserves more attention and study as we work to develop a better understanding of what causes ALS. Importantly, the general population can be exposed to diesel exhaust from traffic pollution. Understanding whether that exposure increases ALS risk is also an important question to pursue.”

The fact that the researchers did not have measurements of participants’ exposure to diesel exhaust, but had to estimate it, could limit the accuracy of the study, they acknowledged.